In certain known processes for removing hydrogen sulfide from gas streams, the hydrogen sulfide is removed by absorption in an aqueous solution of a catalytic reagent, such as a vanadium compound or an iron chelate. The reagent effects oxidation of the hydrogen sulfide to solid sulfur, which precipitates in the aqueous liquid. In continuous operation of such processes, the solid sulfur must be separated from the reagent solution.
Although the separation of the solid sulfur from the reagent can be carried out in any appropriate manner, e.g., by filtration or centrifuging, it is preferred when producing large amounts of sulfur to concentrate the sulfur into a slurry containing 15-20% by weight of sulfur, and to pass the slurry through a melter in which the sulfur is melted, following which the molten sulfur is removed from the aqueous liquid by gravity phase separation. This method of separation has several advantages over other methods, e.g., filtration, in that it minimizes the loss of catalytic reagent which would otherwise occur in the moist filter cake, and in addition, facilitates handling of large quantities of sulfur product.
Prior methods for liquefying sulfur in an aqueous slurry have typically involved passing the slurry through an appropriate heater, such as a shell-and-tube heat exchanger having horizontal tubes, and conveying the heated effluent to a separator in which phase separation occurs, the supernatant aqueous catalytic reagent being recycled to the process, and the lower liquid sulfur phase being transferred by appropriate means to storage. It was found, however, in such operation that if the concentration of solid sulfur in the suspension exceeded relatively low values, e.g., 5-10%, the solid sulfur had a tendency to plug the tubes of the exchanger. Further, the efficiency of separation in the separating vessel was poor, since the relatively high velocity of the aqueous phase, passing vertically through the separator, had a tendency to entrain small particles of sulfur therein and thus lead to operating difficulties in other sections of the process.